Photographic camera lens system having a short total length

ABSTRACT

A behind-stop type photographic camera lens system designed for an aperture ratio of F/2.8, a field angle of 60°, a short total length less than 0.37 f and favorably corrected aberrations, and comprising a first positive meniscus lens component, a second positive meniscus lens component, a third negative lens component, a fourth cemented lens component consisting of a biconvex lens element and a negative lens element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a behind-stop type photographic cameralens system designed for an aperture ratio of F/2.8, field angle of 60°and a short total length.

2. Description of the Prior Art

Almost all the conventional behind-stop type lens systems for 35 mmphotographic cameras had relatively narrow field angles or, whendesigned for relatively wide field angles, large telephoto ratios (ratioof distance measured from the front side to the back focal pointrelative to focal length of lens systems), thereby prolonging theirtotal lengths. When it is attempted to design a behind-stop typephotographic camera lens system so as to have a small telephoto ratioand a wide field angle, on the other hand, marginal rays becomeinsufficient. If lens diameter is increased to obtain sufficientmarginal rays, it will be impossible to design a compact lens system.Japanese Published Examined Patent Application No. 15462/1966 and No.26670/1971 have already disclosed photographic camera lens systems whichare similar to Tesser type and comprise two positive lens components, anegative lens component and a positive cemented lens component. In theselens systems, however, the cemented surface in said positive cementedcomponent is convex on the object side, thereby unavoidably aggravatingastigmatism.

SUMMARY OF THE INVENTION

A general object of the present invention is to provide a compact lenssystem for photographic cameras which has an aperture ratio of F/2.8, arelatively wide field angle of 60° and a short total length of Σd<0.37fand wherein various aberrations are favorably corrected.

The photographic camera lens system according to the present inventionhas such a composition as shown in FIG. 1, and comprises a firstpositive lens component having high power which is effective to design acompact lens system having a wide field angle so far unavailable and afourth lens component having a cemented surface curved in the reversedirection as compared with the ordinary Tesser type lens so as tofavorably correct various aberrations. Said lens system is therefore sodesigned as to favorably correct offaxial aberrations as well ascurvature of astigmatism and asymmetry of coma.

The lens system according to the present invention comprises a firstpositive meniscus lens component, a second positive meniscus lenscomponent, a third negative lens component and a fourth cemented lenscomponent consisting of a biconvex lens element and a negative lenselement, and is characterized in that it satisfies the followingconditions:

    1.86≦φ.sub.1 +φ.sub.2 ≦2.01          (1)

    0.60≦φ.sub.1 ≦0.86                       (2)

    1.75≦n.sub.2                                        ( 3)

    r.sub.8 <0                                                 (4)

    1.4≦φ.sub.(67) /φ.sub.(45) ≦1.9      (5)

wherein the reference symbols represent as defined below:

r₁ through r₉ : radii of curvature on the respective lens elements

d₁ through d₈ : thicknesses of the respective lens elements andairspaces therebetween

n₁ through n₉ : refractive indices of the respective lens elements andairspaces therebetween (in the order from the object side)

φ₁ and φ₂ : refractive powers of the first and second lens componentsφ.sub.(45) and φ.sub.(67) values defined by the following formulae:##EQU1##

Of the conditions mentioned above, the conditions (1) and (2) definerefractive powers of the first and second lens components so as toshorten total length of the lens system and prevent various aberrationsfrom being aggravated.

If φ₁ +φ₂ is smaller than 1.86 in the condition (1), it will beimpossible to minimize telephoto ratio. If φ₁ +φ₂ is larger than 2.01,in contrast, it will be effective for designing a compact lens systembut spherical aberration produced by the first and second lens componentwill be undercorrected. In order to correct this spherical aberration,it will be required to impart a large refractive power to the objectside surface r₅ of the third lens component. In such a case, however,astigmatism and coma will be aggravated by the air lens between thesecond and third lens components (the airspace between the surfaces r₄and r₅ serving just like a concave lens element). If φ₁ is smaller than0.60 in the condition (2), total length of the lens system isunavoidably prolonged, making it impossible to design a compact lenssystem. It is desirable that φ₁ be as large as possible to design acompact lens system. If φ₁ is larger than 0.86, however, sphericalaberration produced by the first lens component will be undercorrectedand cannot be corrected favorably even by enhancing refractive index ofthe first lens component.

The condition (3) is required for preventing spherical aberration frombeing aggravated by the first lens component. Describing in details, itis necessary to give a large value to φ₁ for designing a compact lenssystem as already explained above, and it is additionally required toselect a refractive index n₂ larger than 1.75 for the first lenscomponent in order to prevent various aberrations from being aggravatedwhen a large value is selected for φ₁. If n₂ is smaller than 1.75,radius of curvature on the object side surface of the first lenscomponent will be minimized for selecting a large value for φ₁ andspherical aberration will be remarkably undercorrected. In order tocorrect the spherical aberration favorably, it will be necessary toweaken refractive power of the second lens component and enhancerefractive power of the air lens having diverging function between thesecond and third lens components. However, either of these measures willincrease astigmatic difference, thereby making it difficult to design alens system having a wide field angle. In contrast to a Tesser type lenssystem comprising a cemented lens component having a convex surface onthe object side, the lens system according to the present inventioncomprises a fourth lens component having a radius of curvature r₈ <0 ona cemented surface which is effective for keeping good symmetry of raysas defined in the condition (4). Especially in a behind-stop type lenssystem, light intensity is largely different between the upper and lowerpencils of the rays to be incident on the marginal portion of the imageplane, and therefore, it is desirable that the surface r₈ be concavetoward the intersecting point between the marginal rays and the opticalaxis in order to keep symmetry with regard to the whole pencil, wherebyit becomes possible to prevent coma and astigmatic difference. If r₈ islarger than 0 in the condition (4), asymmetry of coma and astigmaticdifference will be aggravated.

The condition (5) is required to properly balance refractive powersbetween the air lenses on both sides of the third lens component (i.e.,the air lens formed by the surfaces r₄ and r₅ as well as that formed bythe surfaces r₅ and r₆), thereby minimizing astigmatism and coma inthese air lenses. In case of a Tesser type lens system, astigmaticdifference and coma are aggravated most in the air lenses on both sidesof a negative lens component, and it is therefore important forcorrecting the above-mentioned aberrations to properly distributerefractive powers between these air lenses. It is therefore necessary toselect φ.sub.(45) and φ.sub.(67) so as satisfy the condition (5),φ.sub.(45) and φ.sub.(67) being determinable by the formulae givenbelow: ##EQU2## If φ.sub.(67) /φ.sub.(45) is larger than 1.9 in thecondition (5), φ.sub.(67) will have a large value and the air lensformed by the surfaces r₆ and r₇ will be strongly convex, wherebyespecially the principal pencil passing through the high portion andlower pencil of the offaxial rays of the third lens component will belargely refracted dwonward on the surface r₆ as compared with the upperpencil passing through the low portion, resulting in aggravation ofcoma. If φ.sub.(67) /φ.sub.(45) is smaller than 1.4, in contrast, theair lens between the surfaces r₄ and r₅ will be strongly convex, wherebythe offaxial rays will pass through high portion of this air lens andangle of incidence will be large, resulting in aggravation of astigmaticdifference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view illustrating the composition of the lenssystem according to the present invention;

FIG. 2 shows curves illustrating the aberration characteristics of theEmbodiment 1;

FIG. 3 illustrates curves visualizing the aberration characteristics ofthe Embodiment 2; and

FIG. 4 illustrates graphs visualizing the aberration characteristics ofthe Embodiment 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, some preferred embodiments of the present invention will bedescribed detailedly with reference to the accompanying drawings:

    ______________________________________                                        Emobidment 1                                                                                        n.sub.1 = 1                                             r.sub.1 = 0.3607                                                                         d.sub.1 = 0.0454                                                                         n.sub.2 = 1.804                                                                            ν.sub.2 = 46.6                          r.sub.2 = 0.4748                                                                         d.sub.2 = 0.0034                                                                         n.sub.3 = 1                                             r.sub.3 = 0.3488                                                                         d.sub.3 = 0.0680                                                                         n.sub.4 = 1.72916                                                                          ν.sub.4 = 54.7                          r.sub.4 = 0.8837                                                                         d.sub.4 = 0.0214                                                                         n.sub.5 = 1                                             r.sub.5 = 9.4861                                                                         d.sub.5 = 0.0340                                                                         n.sub.6 = 1.68893                                                                          ν.sub.6 = 31.1                          r.sub.6 = 0.2652                                                                         d.sub.6 = 0.0611                                                                         n.sub.7 = 1                                             r.sub.7 = 0.8193                                                                         d.sub.7 = 0.0997                                                                         n.sub.8 = 1.72916                                                                          ν.sub.8 = 54.7                          r.sub.8 = -0.3572                                                                        d.sub.8 = 0.0240                                                                         n.sub.9 = 1.51633                                                                          ν.sub.9 = 64.2                          r.sub.9 = 58.7836                                                                      f = 1 , φ.sub.1 = 0.631 , φ.sub.2 = 1.332                             φ.sub.(45) = -0.898 , φ.sub.(67) = -1.567                    Embodiment 2                                                                                        n.sub.1 = 1                                             r.sub.1 = 0.3397                                                                         d.sub.1 = 0.0531                                                                         n.sub.2 = 1.7725                                                                           ν.sub.2 = 49.6                          r.sub.2 = 0.5065                                                                         d.sub.2 = 0.0015                                                                         n.sub.3 = 1                                             r.sub.3 = 0.3567                                                                         d.sub.3 = 0.0555                                                                         n.sub.4 = 1.72916                                                                          ν.sub.4 = 54.7                          r.sub.4 = 0.7743                                                                         d.sub.4 = 0.0209                                                                         n.sub.5 = 1                                             r.sub.5 = 43.1401                                                                        d.sub.5 = 0.0252                                                                         n.sub.6 = 1.6668                                                                           ν.sub.6 = 33.0                          r.sub.6 = 0.2580                                                                         d.sub.6 = 0.0641                                                                         n.sub.7  = 1                                            r.sub.7 = 0.9574                                                                         d.sub.7 = 0.1083                                                                         n.sub.8 = 1.72916                                                                          ν.sub.8 = 54.7                          r.sub.8 = -0.3942                                                                        d.sub.8 = 0.0173                                                                         n.sub.9 = 1.51112                                                                          ν.sub.9 = 60.5                          r.sub.9 = -12.7838                                                                     f = 1 , φ.sub.1 = 0.847 , φ.sub.2 = 1.157                             φ.sub.(45) = -0.920 , φ.sub.(67) = -1.698                    Embodiment 3                                                                                        n.sub.1 = 1                                             r.sub.1 = 0.3467                                                                         d.sub.1 = 0.0483                                                                         n.sub.2 = 1.7725                                                                           ν.sub.2 = 49.6                          r.sub.2 = 0.4685                                                                         d.sub.2 = 0.0033                                                                         n.sub.3 = 1                                             r.sub.3 = 0.3674                                                                         d.sub.3 = 0.0623                                                                         n.sub.4 = 1.72916                                                                          ν.sub.4 = 54.7                          r.sub.4 = 0.8693                                                                         d.sub.4 = 0.0229                                                                         n.sub.5 =  1                                            r.sub.5 = -3.7715                                                                        d.sub.5 = 0.0307                                                                         n.sub.6 = 1.6668                                                                           ν.sub.6 = 33.0                          r.sub.6 = 0.2767                                                                         d.sub.6 = 0.0565                                                                         n.sub.7 = 1                                             r.sub.7 = 0.9024                                                                         d.sub.7 = 0.0863                                                                         n.sub.8 = 1.72916                                                                          ν.sub.8 = 54.7                          r.sub.8 = -0.3695                                                                        d.sub.8 = 0.0200                                                                         n.sub.9 = 1.51112                                                                          ν.sub.9 = 60.5                          r.sub.9 = -4.0819                                                                      f = 1 , φ = 0.678 , φ.sub.2 = 1.208                                   φ.sub.(45) = -1.018 , φ.sub.(67) = -1.493                    ______________________________________                                    

wherein the reference symbol f represents focal length of the lenssystem as a whole, the reference symbols r₁ through r₉ designate radiiof curvature on the surfaces of the respective lens elements, thereference symbols d₁ through d₆ denote thicknesses of the respectivelens elements and airspaces therebetween, the reference symbols n₁through n₉ represent refractive indices of the respective lens elementsand airspaces therebetween, and the reference symbols ν₁ through ν₉designate Abbe's numbers of the respective lens elements, saidrefractive indices being defined for the lens elements and airspaces inthe order consecutively from the object side taking refractive index ofair as 1.

The aberration characteristics of the Embodiments 1 through 3 arevisualized in FIG. 2 through FIG. 4 respectively.

As is understood from the foregoing descriptions and drawingsillustrating the embodiments, the lens system according to the presentinvention is a very compact photographic camera lens systems comprisinga behind stop which has a relatively wide field angle of 60° and whereinvarious aberrations are favorably corrected. Compared in the table shownbelow are telephoto ratio (m) and ratio (k) of total length relative tothe maximum height between the lens systems disclosed by the publishedexamined applications mentioned at the beginning and that according tothe present invention.

                  TABLE                                                           ______________________________________                                                           m      k                                                   ______________________________________                                        Japanese Published Examined                                                   Patent Application                                                            No. 15462/1966       1.205    2.267                                           Japanese Published Examined                                                   Patent Application                                                            No. 266670/1971                                                                Embodiment 1        1.056    2.751                                            Embodiment 2        1.055    1.983                                           Present Invention    1.079    1.75                                            ______________________________________                                    

In contrast to the two conventional lens systems designed for a fieldangle narrower than 56°, the lens system according to the presentinvention has a large field angle of 60°. Further, it is deemed thatthese two conventional lens systems comprises stops which are arrangedinside said lens systems. Contrastingly, the lens system according tothe present invention is designed for a telephoto ratio similar to thatof the conventional lens system as shown in the above table in spite ofthe fact that it is of the behind stop type which can hardly be designedas a compact and desirable lens system. Further, ratio (k) of totallength relative to maximum height is compared in the table since it isconsidered improper to judge compactness of lens system having differentfield angles by comparing telephoto ratios. The lens system according tothe present invention is very compact as is clear from the data shown inthe above table.

I claim:
 1. A photographic camera lens system having a short totallength comprising a first positive meniscus lens component, a secondpositive meniscus lens component, a third negative lens component and afourth cemented lens component consisting of a biconvex lens element anda negative lens element, and said lens system satisfying the followingconditions:

    1.86≦φ.sub.1 +φ.sub.2 ≦2.01          (1)

    0.60≦φ.sub.1 ≦0.86                       (2)

    1.77≦n.sub.2 ≦1.81                           (3)

    -0.40f≦r.sub.8 23 -0.35f                            (4)

    1.4≦φ.sub.(67) /φ.sub.(45) ≦1.9      (5)

wherein the reference symbols r₁ through r₉ represent radii of curvatureon the surfaces of the respective lens elements, the reference symbolsd₁ through d₈ designate thicknesses of the respective lens elements andairspaces therebetween, the reference symbols n₁ through n₉ denoterefractive indices of the lens elements and airspaces therebetween, thereference symbols φ₁ and φ₂ represent refractive powers of the first andsecond lens components, reference symbols φ.sub.(45) and φ.sub.(67)represent values which are defined by the following formulae: ##EQU3##2. A photographic camera lens system according to claim 1 having thefollowing numerical data:

    ______________________________________                                                         n.sub.1 = 1                                                  r.sub.1 = 0.3607                                                                 d.sub.1 = 0.0454                                                                            n.sub.2 = 1.804                                                                            ν.sub.2 = 46.6                               r.sub.2 = 0.4748                                                                 d.sub.2 = 0.0034                                                                            n.sub.3 = 1                                                  r.sub.3 = 0.3488                                                                 d.sub.3 = 0.0680                                                                            n.sub.4 = 1.72916                                                                          ν.sub.4 = 54.7                               r.sub.4 = 0.8837                                                                 d.sub.4 = 0.0214                                                                            n.sub.5 = 1                                                  r.sub.5 = -9.4861                                                                d.sub.5 = 0.0340                                                                            n.sub.6 = 1.68893                                                                          ν.sub.6 = 31.1                               r.sub.6 = 0.2652                                                                 d.sub.6 = 0.0611                                                                            n.sub.7 = 1                                                  r.sub.7 = 0.8193                                                                 d.sub.7 = 0.0997                                                                            n.sub.8 = 1.72916                                                                          ν.sub.8 = 54.7                               r.sub.8 = -0.3572                                                                d.sub. 8 = 0.0240                                                                           n.sub.9 = 1.51633                                                                          ν.sub.9 = 64.2                               r.sub.9 = 58.7836                                                             f = 1, φ.sub.1 = 0.631, φ.sub.2 = 1.332                               φ.sub.(45) = -0.898, φ.sub.(67) = -1.567                              ______________________________________                                    

wherein the reference symbol f represetns focal length of the lenssystem as a whole, the reference symbols ν₁ through ν₉ designate radiiof curvature on the surfaces of the respective lens elements, thereference symbols d₁ through d₆ denote thicknesses of the respectivelens elements and airspaces therebetween, the reference symbols n₁through n₉ represent refractive indices of the respective lens elementsand airspaces therebetween, and the reference symbols ν₁ through ν₉designate Abbe's numbers of the respective lens elements, saidrefractive indices being defined for the lens elements and airspaces inthe order consecutively from the object side taking refractive index ofair as 1, reference symbols φ₁, φ₂, φ.sub.(45), φ.sub.(67) representvalues defined by the following formulae: ##EQU4##
 3. A photographiccamera lens system according to claim 1 having the following numericaldata:

    ______________________________________                                                         n.sub.1 = 1                                                  r.sub.1 = 0.3397                                                                 d.sub.1 = 0.0531                                                                            n.sub.2 = 1.7725                                                                           ν.sub.2 = 49.6                               r.sub.2 = 0.5065                                                                 d.sub.2 = 0.0015                                                                            n.sub.3 = 1                                                  r.sub.3 = 0.3567                                                                 d.sub.3 = 0.0555                                                                            n.sub.4 = 1.72916                                                                          ν.sub.4 = 54.7                               r.sub.4 = 0.7743                                                                 d.sub.4 = 0.0209                                                                            n.sub.5 = 1                                                  r.sub.5 = 43.1401                                                                d.sub.5 = 0.0252                                                                            n.sub.6 = 1.6668                                                                           ν.sub.6 = 33.0                               r.sub.6 = 0.2580                                                                 d.sub.6 = 0.0641                                                                            n.sub.7 = 1                                                  r.sub.7 = 0.9574                                                                 d.sub.7 = 0.1083                                                                            n.sub.8 = 1.72916                                                                          ν.sub.8 = 54.7                               r.sub.8 = -0.3942                                                                d.sub.8 = 0.0173                                                                            n.sub.9 = 1.51112                                                                          ν.sub.9 = 60.5                               r.sub.9 = -12.7838                                                            f = 1, φ.sub.1 = 0.847, φ.sub.2 = 1.157                               φ.sub.(45) = -0.920, φ.sub.(67) = -1.698                              ______________________________________                                    

wherein the reference symbol f represetns focal length of the lenssystem as a whole, the reference symbols r₁ through r₉ designate radiiof curvature on the surfaces of the respective lens elements, thereference symbols d₁ through d₆ denote thicknesses of the respectivelens elements and airspaces therebetween, the reference symbols n₁through n₉ represent refractive indices of the respective lens elementsand airspaces therebetween, and the reference symbols ν₁ through ν₉designate Abbe's numbers of the respective lens elements, saidrefractive indices being defined for the lens elements and airspaces inthe order consecutively from the object side taking refractive index ofair as 1, reference symbols φ₁, φ₂, φ.sub.(45), φ.sub.(67) representvalues defined by the following formulae: ##EQU5##
 4. A photographiccamera lens system according to claim 1 having the following numericaldata:

    ______________________________________                                                         n.sub.1 = 1                                                  r.sub.1 = 0.3467                                                                 d.sub.1 = 0.0483                                                                            n.sub.2 = 1.7725                                                                           ν.sub.2 = 49.6                               r.sub.2 = 0.4685                                                                 d.sub.2 = 0.0033                                                                            n.sub.3 = 1                                                  r.sub.3 = 0.3674                                                                 d.sub.3 = 0.0623                                                                            n.sub.4 = 1.72916                                                                          ν.sub.4 = 54.7                               r.sub.4 = 0.8693                                                                 d.sub.4 = 0.0229                                                                            n.sub.5 = 1                                                  r.sub.5 = -3.7715                                                                d.sub.5 = 0.0307                                                                            n.sub.6 = 1.6668                                                                           ν.sub.6 = 33.0                               r.sub.6 = 0.2767                                                                 d.sub.6 = 0.0565                                                                            n.sub.7 = 1                                                  r.sub.7 = 0.9024                                                                 d.sub.7 = 0.0863                                                                            n.sub.8 = 1.72916                                                                          ν.sub.8 = 54.7                               r.sub.8 = -0.3695                                                                d.sub.8  = 0.0200                                                                           n.sub.9 = 51112                                                                            ν.sub.9 = 60.5                               r.sub.9 = -4.0819                                                             f = 1, φ.sub.1 = 0.678, φ.sub.2 = 1.208                               φ.sub.(45) = -1.018, φ.sub.(67) = -1.493                              ______________________________________                                    

wherein the reference symbol f represents focal length of the lenssystem as a whole, the reference symbols r₁ through r₉ designate radiiof curvature on the surfaces of the respective lens elements, thereference symbols d₁ through d₆ denote thicknesses of the respectivelens elements and airspaces therebetween, the reference symbols n₁through n₉ represent refractive indices of the respective lens elementsand airspaces therebetween, and the reference symbols ν₁ through ν₉designate Abbe's numbers of the respective lens elements, saidrefractive indices being defined for the lens elements and airspaces inthe order consecutively from the object side taking refractive index ofair as 1, reference symbols φ₁, φ₂, φ.sub.(45), φ.sub.(67) representvalues defined by the following formulae: ##EQU6##